9. Relative risk and odds ratio

What are the 2 approaches of measurement of excess risk?

1. The ratio of the risks 2. The difference in the risks

Define association

Association: a statistical relationship between two or more variables.

How is odds ratio interpreted?

If OR = 1, exposure is not related to disease - no association; independent. If RR < 1, exposure is negatively related to the disease. If RR > 1, exposure is positively related to disease. Primary group = numerator

How is the relative risk interpreted?

If RR = 1, the risk of disease is equal in each group. If RR < 1, the primary group has a lower risk of disease. If RR > 1, the primary group has a higher risk of disease. Primary group = numerator

Can a case-control study identify relative risk? Why?

In a case-control study, we do not know the incidence in the exposed population or the incidence in the non-exposed population. This is based on the fact that these studies start with diseased people (cases) and non-diseased people (controls). Hence, in a case-control study we cannot calculate the relative risk directly.

Define odds ratio

Ratio of odds of disease in the present of a risk factor (exposed) to the odds of disease in the absence of a risk factor (unexposed).

Define risk

Risk can be defined as the probability of an event (such as developing a disease) occurring.

Define absolute risk

The incidence of a disease in a population is termed the absolute risk. Absolute risk can indicate the magnitude of the risk in a group of people with a certain exposure, but because it does not take into consideration the risk of disease in non-exposed individuals, it does not indicate whether the exposure is associated with an increased risk of the disease.

How do we determine whether a certain disease is associated with a certain exposure?

To determine whether such an association exists, we must determine, using data obtained in case-control and cohort studies, whether there is an excess risk of the disease in persons who have been exposed to a certain agent.

How to definitively determine association?

by determining there is an excess risk of diseased in the exposed vs. non-exposed groups.

What's the difference in odds ratio of a case-control vs. cohort studies?

in cohort studies it looks prospectively of whether cases are exposed. In case-control studies it is more retrospective (prone to recall bias) of whether cases were exposed.

Define relative risk

the probability of an event (developing a disease) occurring in exposed people vs. non exposed. I.e. = the ratio of the probabilities